YSI SonTek ADVField, Technical Documentation Manual

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SonTek/YSI
ADVField Software Manual (September 1, 2001) 14
Graphical Display
The main portion of the screen displays two plots. The upper plot represents the mean value for
signal-to-noise ratio (SNR) from the three receivers (in dB) and the mean value for correlation
for the three receivers (percent). The lower plot is the time-series of the three velocity compo-
nents. Both graphs are plotted left to right against time. A vertical bar identifies the current (most
recent) point. If the full span of the plot is reached (right end), plotting resumes on the left side.
If the ADV has the optional pressure sensor installed, the lower graph will include a fourth plot
for pressure data. This pressure data is plotted in units of counts with the axis set to full scale
(bottom of the plot corresponds to zero pressure, top corresponds to maximum pressure).
Active Keys
Several active keys (or key combinations) may be used during data collection. Note: Two of the
keys (Ctrl+S and Ctrl+Q) affect data recording while the program is in the data acquisition mode.
F1 - Display Probe
(Multiple choice)
Not used by ADVField systems.
F3 - Change Time Span
(Multiple choice)
This key lets you change the time span of the real-time trace from several preset alternatives.
F4 - Change Trace Vel
(Multiple choice)
This key lets you change which velocity components are plotted. You can display all three com-
ponents simultaneously or any single component.
F5 - Change Vel Scale
(Multiple choice)
This key lets you change the full velocity scale of the trace from several preset alternatives.
F6 - Filter
(Multiple choice)
The data shown in the tabular display are filtered to allow you to estimate the mean data values
over a time scale that is determined by the filter setting. <F6> allows you to change the filter time
constant from several preset alternatives.
The filter used for the tabular display is a first-order recursive filter of the form:
y(i+1)=y(i)*a+x(i+1)*(1-a); where y(1) = x(1)
and where x(i) are the individual data samples from the ADV (for velocity, signal-to-noise ratio,
and correlation). The values y(i) are the mean values for each of these variables shown in the
tabular display. The standard deviation of velocity data is calculated as:
y2(i+1)=y2(i)*a+x(i+1)*x(i+1)*(1-a); where y2(1) = x(1)*x(1);
sqrt(y2(i+1) - y(i+1)*y(i+1))
If
dt
is the sampling interval (1/sampling frequency), and
Nfilt
is the total number of samples
within the filter width (Tfilt) (i.e., Nfilt=Tfilt/dt), then
a = (Nfilt-1)/Nfilt.
For example, for a 10-second filter when sampling at 25 Hz, a = 249/250. If a<0, a=0.